1. Field of the Invention
This invention relates generally to measurement of gas pressures and more particularly to gas pressure measurement devices used with vacuum-type devices.
2. Description of Related Art
Many electronic devices today employ evacuated chambers, such as traveling-wave tubes, klystrons, multipactors and plasma generators, for example. These vacuum-type electronic devices require that undesired foreign gases be limited to prescribed amounts for the particular device to operate efficiently. For example, a traveling-wave tube is evacuated to a pressure typically of less than about 10.sup.-8 torr. A traveling-wave tube typically includes an evacuated chamber wherein a cathode generated electron beam which interacts with a wave traveling along a slow-wave structure, transfering energy to the wave. If the chamber should leak, atoms or molecules of any gas entering the chamber will collect on the surface of the cathode while the device is in a storage, or "off", condition. The accumulation of foreign matter on the cathode may cause sluggish turn-on performance or even a failure to turn on at all. Vacuum-type devices often have a long shelf time and therefore are susceptable to contamination and consequently failure at turn-on, particularly vacuum devices requiring fast turn on. Furthermore, vacuum-type devices such as traveling-wave tubes, klystrons, and plasma generators are typically employed in aircraft or spacecraft in which failures could be difficult if not impossible to remedy. Accordingly, sluggish turn-on or failure to turn on could lead to the failure of an entire system that employs such vacuum devices.
Therefore, an accurate and easy to use pressure measurement device is needed to screen vacuum devices for contamination before they are switched on. Devices have been developed to measure the pressure in vacuum-type devices. The devices available, however, are typically large and cumbersome or employ high-speed circuitry or high voltage to operate. For example, the Bayard Alpert gauge is a conventional pressure gauge. However, this gauge is not compact because of its characteristic geometry. Additionally, this gauge uses high voltages which generate x-rays that interfere with the pressure sensitive signal. A simple compact device to determine gas pressure in evacuated devices would greatly advance the art.
Additional background of interest may be found in an article by J. H. Malmberg and C. F. Driscoll, "Long-Time Containment of a Pure Electron Plasma", Vol. 44, No. 10, Physical Review Letters 654-57 (Mar. 10, 1980). This article discloses an arrangement designed to contain a single species plasma for studying a wide variety of plasma phenomena. Plasma is held for a variable time t within a grounded cylinder between negatively biased gating rings. After time t, one of the gating rings is gated to ground and the plasma exits the cylinder. The total charge remaining after time t is measured (upon exiting) to determine how much of the plasma was lost during confinement. Experimental results on long time containment of a pure electron plasma is reported in this article. This article, however, has nothing to do with measuring gas pressure or an arrangement to measure gas pressure.